Connotations of なら vs たら in conditional clauses

Question

I am wondering about the choice of, and general necessity of, なら in the following sentence.

ドイツでは、ウイルスがうつらないように気をつけているなら、店を開くことができます。(from NHK Easy)

* In Germany, businesses may remain open if they are careful not to spread the virus. (my trans.)

According to DBJG, なら means roughly 'under the condition that something is true'. How does this work in the context of the above sentence, in particular why would たら not be appropriate, since (in my mind) any if-clause always assumes its own validity.

Does the なら carry a sense of "actually" or "really" here? For example, would it be more accurate to translate the sentence as "... if the businesses are really ensuring the virus doesn't spread"? Or does なら contain a sense of "so long as", i.e. suggesting that the condition is liable to change over time, "...as long as the businesses are ensuring the virus doesn't spread."?

Answer 1

It's a matter of BEFORE / AFTER.

なら is like BEFORE you do Y, the precondition X must be met. I tell my kids, おそといくなら、くつはこうね！ "Before you can go outside, you have to put shoes on!"

たら is like AFTER you do Y, you must do Z. I say to my kids, ごはんたべたら、はをみがこうね。 When you are done eating dinner, brush your teeth.

Answer 2

I know it was taken from an NHK site but 気をつけているなら doesn’t sound too natural to me.

I would say:

ウイルスがうつらないように気をつけていれば、店を開くことができます。

The article is deliberately written in easy Japanese so non-advanced learners or foreign residents can understand. Maybe れば is not considered easy enough.

Besides, it is not very natural to understand 気をつけているなら as referring to something that should happen after the opening of the shops as expected by なら. This is because of the use of 〜ている. It would be more natural to understand it as a current state (that obviously is expected to continue beyond the opening of the shops), despite なら. This is precisely the reason I find 気をつけていれば more natural. If 気をつけているなら is to be interpreted as a future condition for the opening of the shops, it does carry a sense of “as long as”.

The following sentence, with the combination of a dictionary form and なら, would be naturally understood as a condition to be satisfied after the opening of the shops.

ウイルスがうつらないように気をつけるなら、店を開くことができます。

As for たら, the following sentence, with the combination of 〜ている and たら (i.e. 〜いていたら), is actually not that bad, although it is more common in certain dialects than in standard Japanese.

ウイルスがうつらないように気をつけていたら、店を開くことができます。

The following, without 〜ている, is grammatical but it doesn’t convey the message it is supposed to.

ウイルスがうつらないように気をつけたら、店を開くことができます。

It sounds as if being careful not to spread the virus is a one-time thing that should happen before the opening of the shops.

Answer 3

Among the conditionals, the special thing with なら is that the preceding (conditional) clause can happen in time after the succeeding (main) clause, which is not the case for others like たら, where the first clause always happens before the second.

So in the case of

ウイルスがうつらないように気をつけているなら、店を開くことができます。

to imply that "being careful" happens after (or maybe rather during) "remaining open", the only correct conditional is なら.

For an overview of the differences between all conditionals see this answer.